Flexible, deformable seals are well known for use in a variety of sealing arrangements, one example of which is shown in U.S. Pat. No. 4,785,850 to Sanchez, the disclosure of which is fully incorporated herein by reference. As best seen in FIG. 1 of that patent, an O-ring gasket 36 rests in a groove which surrounds the outside of a soap cup 20. The soap cup can be screwed into a valve body and is sealed against that body when the gasket is pressed against a flat surface of the valve body. Water and soap under pressure within the soap cup are contained in the soap cup by the deformed O-ring gasket pushing against the soap cup and the valve body's flat surface. In this arrangement, the soap cup can be easily installed or removed, and the O-ring gasket is held in place because it must be stretched slightly to fit around the outside circumference of the soap cup.
Unfortunately, the arrangement is also prone to leaks. Fluid within the soap cup is pushed out towards the O-ring and to the contact area between the gasket and the valve body's flat surface. Unless the gasket is already tightly pressed against the flat surface, the fluid pressure is enough to press the gasket away and create an opening between the gasket and the valve body's flat surface, allowing the fluid to leak out. To completely ensure against leaks, the soap cup must be screwed down very tightly, which is inconvenient to do by hand. In addition, the soap cup's groove stores pressure below the gasket. Even when the fluid pressure in the soap cup is released, the fluid trapped in the groove will continue to push the gasket against the valve body making the soap cup difficult to remove. Finally, the gasket will often stretch over time and fail to hug the outside circumference tightly enough to stay in place when the soap cup is removed.
Another know sealing arrangement is shown in U.S. Pat. No. 2,157,983 to Glougie. In this patent, a chamber is closed by a platen and sealed by an O-ring mounted in the chamber walls. Passages through the walls of the chamber conduct pressurized fluid within the chamber to the underside of the the seal to push the seal up against the platen. This arrangement reduces the leakage problem above, but the passages shown are difficult and expensive to produce, especially in a thin walled chamber and especially with high speed plastic injection molding. In addition, the O-ring seal as shown in FIG. 3 of Glougie must have a peculiar shape and be very closely matched to the recess in the chamber wall in which the O-ring sits.